In the medical field, various types of automatic, body-implantable devices are known and commercially-available. One of the more common types of body-implantable devices is the cardiac pacemaker, which operates to deliver electrical stimulating pulses to a patient's heart. A cardiac pacemaker is disclosed, for example, in U.S. Pat. No. 5,052,388 to Sivula et al, entitled "Method and Apparatus for Implementing Activity Sensing in a Pulse Generator." Implantable cardioverters, defibrillators, and drug pumps are other examples of presently available automatic implantable devices. An example of a combination pacemaker/cardioverter/defibrillator is described in U.S. Pat. No. 5,179,946 to Weiss, entitled "Apparatus and Method for Arrhythmia Detection by Variations in the Transcardiac Impedance Between Defibrillation Patches."
It has also been proposed in the prior art to provide implantable tissue stimulators for controlling nerve or muscle response, for alleviating pain, or to treat various neurological and/or physiological disorders, such as cerebral palsy, epilepsy, and the like. Examples of such devices are discussed in the following U.S. patents: U.S. Pat. No. 4,232,679 to Schulman, entitled "Programmable Human Tissue Stimulator;" U.S. Pat. No. 4,735,204 to Sussman et al., entitled "System for Controlling an Implanted Neural Stimulator;" and in U.S. Pat. No. 4,793,353 to Borkan, entitled "Non-Invasive Multiprogrammable Tissue Stimulator and Method. " A commercially-available example of an implantable tissue stimulator is the Model 7425 Itrel.TM. 3 Implantable Pulse Generator, manufactured by Medtronic, Inc., Minneapolis, Minn. The Itrel.TM. 3 is a spinal cord stimulating system prescribed to alleviate chronically-recurring pain.
It is very common for automatic implantable devices to be non-invasively controllable by means of an external programming apparatus of some sort, so that an implanted device's operational modes and/or parameters may be adjusted, for example to optimize its therapeutic efficacy or in response to post-implant changes in a patient's condition. Often, such non-invasive control is exercised by a physician in a clinical setting.
Perhaps one of the simplest arrangements for facilitating non-invasive control of an implanted device involves providing a magnetic reed switch in the implantable device. After implant, the reed switch can be actuated (closed) by placing a magnet over the implant site. Reed switch closure may then be used, for example, to alternately activate and deactivate the device. Alternatively, some variable parameter of the device (e.g., the pacing rate of an implantable cardiac pacemaker) can be adjusted up or down by incremental amounts based upon the duration of the reed switch closure interval. Many different schemes utilizing a reed switch to adjust operational parameters of medical devices have been developed. See, for example, U.S. Pat. No. 3,311,111 to Bowers; U.S. Pat. No. 3,518,997 to Sessions; U.S. Pat. No. 3,623,486 to Berkovits; U.S. Pat. No. 3,631,860 to Lopin; U.S. Pat. No. 3,738,369 to Adams et al., U.S. Pat. No. 3,805,796 to Terry, Jr.; U.S. Pat. No. 4,066,086 to Alferness et al.; and the above-reference U.S. Pat. No. 4,735,204 to Sussman et al.
Although the relatively simple reed-switch closure arrangement is suitable for the purposes of controlling or adjusting a limited number of operational parameters or modes of an implanted device, it has proven beneficial to provide a means for more efficiently communicating programming information to an implanted device, so that a greater number of the device's operating modes and parameters can be adjusted. In state-of-the-art cardiac pacemakers, for example, a partial list of the types of programmable parameters includes: upper and lower pacing rate limits, stimulating pulse width and/or amplitude, sense amplifier sensitivity, pacing mode, activity- or rate-response settings (e.g., pacing rate acceleration and deceleration, activity threshold, activity detection criteria, and the like), A-V delay times, refractory and blanking periods, and so on. It has also proven desirable for implanted devices themselves to be able to communicate information to an external programming apparatus.
In response to the foregoing considerations, various telemetry systems for providing the necessary communications channels between an external unit and an implanted device have been developed. Telemetry systems are disclosed, for example, in the following U.S. patents: U.S. Pat. No. 4,539,992 to Calfee et al. entitled "Method and Apparatus for Communicating With Implanted Body Function Stimulator"; U.S. Pat. No. 4,550,732 to Batty Jr. et al. entitled "System and Process for Enabling a Predefined Function Within An Implanted Device"; U.S. Pat. No. 4,571,589 to Slocum et al. entitled "Biomedical Implant With High Speed, Low Power Two-Way Telemetry"; U.S. Pat. No. 4,676,248 to Berntson entitled "Circuit for Controlling a Receiver in an Implanted Device"; U.S. Pat. No. 5,127,404 to Wyborny et al. entitled "Telemetry Format for Implanted Medical Device"; U.S. Pat. No. 4,211,235 to Keller, Jr. et al. entitled "Programmer for Implanted Device"; U.S. Pat. No. 4,374,382 to Markowitz entitled "Marker Channel Telemetry System for a Medical Device"; and U.S. Pat. No. 4,556,063 to Thompson et al. entitled "Telemetry System for a Medical Device".
Typically, telemetry systems such as those described in the above-referenced patents are employed in conjunction with an external programming/processing unit. One programmer for non-invasively programming a cardiac pacemaker is described in its various aspects in the following U.S. patents to Hartlaub et al., each commonly assigned to the assignee of the present invention and each incorporated by reference herein: U.S. Pat. No. 4,250,884 entitled "Apparatus For and Method Of Programming the Minimum Energy Threshold for Pacing Pulses to be Applied to a patient's Heart"; U.S. Pat. No. 4,273,132 entitled "Digital Cardiac Pacemaker with Threshold Margin Check"; U.S. Pat. No. 4,273,133 entitled Programmable Digital Cardiac Pacemaker with Means to Override Effects of Reed Switch Closure"; U.S. Pat. No. 4,233,985 entitled "Multi-Mode Programmable Digital Cardiac Pacemaker"; U.S. Pat. No. 4,253,466 entitled "Temporary and Permanent Programmable Digital Cardiac Pacemaker"; and U.S. Pat. No. 4,401,120 entitled "Digital Cardiac Pacemaker with Program Acceptance Indicator".
Aspects of the programmer that is the subject of the foregoing Hartlaub et al. patents (hereinafter "the Hartlaub programmer") are also described in U.S. Pat. No. 4,208,008 to Smith, entitled "Pacing Generator Programming Apparatus Including Error Detection Means" and in U.S. Pat. No. 4,236,524 to Powell et al., entitled "Program Testing Apparatus". The Smith '008 and Powell et al. '524 patents are also incorporated by reference herein in their entirety.
Most commonly, telemetry systems for implantable medical devices employ a radio-frequency (RF) transmitter and receiver in the device, and a corresponding RF transmitter and receiver in the external programming unit. Within the implantable device, the transmitter and receiver utilize a wire coil as an antenna for receiving downlink telemetry signals and for radiating RF signals for uplink telemetry. The system is modelled as an air-core coupled transformer. Examples of such a telemetry system are shown in the above-referenced Thompson et al. '063 and Hartlaub et al. '120 patents.
In order to communicate digital data using RF telemetry, a digital encoding scheme such as is described in U.S. Pat. No. 5,127,404 to Wyborny et al. entitled "Improved Telemetry Format" is used. In particular, for downlink telemetry a pulse interval modulation scheme may be employed, wherein the external programmer transmits a series of short RF "bursts" or pulses in which the during of an interval between successive pulses (e.g., the interval from the trailing edge of one pulse to the trailing edge of the next) encodes the data. In particular, a shorter interval encodes a digital "0" bit while a longer interval encodes a digital "1" bit.
For uplink telemetry, a pulse position modulation scheme may be employed to encode uplink telemetry data. For pulse position modulation, a plurality of time slots are defined in a data frame, and the presence or absence of pulses transmitted during each time slot encodes the data. For example, a sixteen position data frame may be defined, wherein a pulse in one of the time slots represents a unique four bit portion of data. The Wyborny et al. '404 patent is hereby incorporated by reference herein in its entirety.
Programming units such as the above-described Hartlaub et al. programmer typically interface with the implanted device through the use of a programming head or programming paddle, a handheld unit adapted to be placed on the patient's body over the implant site of the patient's implanted device. A magnet in the programming head effects reed switch closure in the implanted device to initiate a telemetry session. Thereafter, uplink and downlink communication takes place between the implanted device's transmitter and receiver and a receiver and transmitter disposed within the programming head.
State-of-the-art implantable medical device programmers, as exemplified by the Model 9760 programming unit, manufactured by Medtronic, Inc., Minneapolis, Minn., facilitate the non-invasive control of a full range of operational and diagnostic functions of implanted devices. Accordingly, such programming units are typically used by physicians or other medical personnel in a clinical setting, so that the patient's condition can be carefully monitored during the programming session. Those of ordinary skill in the art will appreciate, however, that in some cases it may be desirable to provide means for allowing the patient to exercise some degree of control over device operation, even outside of the clinical setting. It is desirable, for example, for a patient with an implanted spinal cord stimulation system to be able to trigger the device to deliver a stimulating pulse whenever the patient experiences an episode of pain that the device is intended to alleviate.
To address the need for patient control of an implanted device, so-called patient programmers, such as the Medtronic Model 7433, were developed. The Model 7433 was designed to facilitate patient control over Medtronic implantable tissue stimulators. In operation, the Model 7433 was placed over the implant site and a downlink telemetry link was established, whereby a single cycle of stimulation could be initiated by the patient.
Although the Model 7433 patient programmer has proven satisfactory for its intended purpose, it is believed that the present invention represents an advancement over the prior art, as exemplified by the Model 7433, in several aspects. In particular, it is believed that no prior art programmer intended for use by patients, has incorporated features in recognition of factors such as the varying characteristics of potential patients who will use a patient programmer, including such potential patients' age, education, dexterity, and physical and mental health.